Apparatus and method for plating wafers, substrates and other articles

ABSTRACT

A plating apparatus and methodology is disclosed that is particularly useful in improving the plating rate, improving the plating of via holes, improving the uniformity of the plating deposition across the surface of the wafer, and minimizing damage to the wafer. With regard to improving the plating rate and the plating of via holes, the plating apparatus and method immerses a wafer in a plating fluid bath and continuously directs plating fluid towards the surface of the wafer. Immersing the wafer in a plating fluid bath reduces the occurrence of trapped gas pockets within via holes which makes it easier to plate them. The continuous directing of plating fluid towards the surface of the wafer increases the ion concentration gradient which is, in turn, increases the plating rate. With regard to improving the uniformity of the plating deposition, the plating apparatus and method effectuate random horizontal fluid flow within the bath to reduce the occurrence of relatively long horizontal fluid flow that causes non-uniform plating deposition across the surface of the wafer.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a Divisional Application of application Ser. No.09/348,768, filed Jul. 7, 1999, now U.S. Pat. No. 6,197,182 which isincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to methods and apparatus for platingwafers, substrates and other articles, and in particular, to methods andapparatus of configuring the fluid dynamics and electrostatics of aplating process in order to provide improved uniformity in platingdeposition, improved plating rates, and improved step coverage of viaholes.

BACKGROUND OF THE INVENTION

Because of recent technological advancements in the fields of computersand telecommunications, there has been a substantial increase in demandfor “high tech” products. Not only do consumers want more sophisticatedcomputer, telecommunication and other “high-tech” systems, they want itat a more economical costs. Because of this consumer desire, high techindustries are gearing their manufacturing techniques to produceproducts that are made as economical as possible, with improvedperformance and reliability.

One of the backbone industries supporting many high tech industries,including the computer and telecommunication fields, involves themanufacturing of semiconductor wafers. Semiconductor wafers are usedextensively for the manufacturing of integrated circuits, semiconductordevices, and other circuits and/or components. The manufacturing of anintegrated circuit or device typically comprises several manufacturingstages, including processing the semiconductor wafer to form the desiredcircuits and/or devices, forming a copper seed layer on the base plateof the semiconductor, plating the copper seed layer with a layer ofcopper having a desired thickness, and dicing the wafers in order toform separate integrated circuits and/or components. The inventiondescribed herein involves the plating aspect of the overall integratedcircuits/devices manufacturing process.

Because of high tech industries' need for manufacturing techniques thateconomically produce products that have improved performance andreliability characteristics, this need is also a driving force in thefield of plating semiconductor wafers. In terms of performance, it isdesired for a method and apparatus for plating semiconductor wafers thatachieves improved uniformity of the plating deposition across thesurface of the wafer. In terms of reliability, it is desired for amethod and apparatus for plating semiconductor wafers that accomplishesthe desired plating of the semiconductor wafer, without subjecting thewafer to unnecessary harsh environments. In terms of manufacturingcosts, it is desired for a method and apparatus for platingsemiconductor wafers that accomplishes the desired plating of thesemiconductor wafer in a relatively fast manner.

These needs are satisfied with the method and apparatus of platingwafers, substrates and other articles in accordance with the inventionas described hereinafter.

SUMMARY OF THE INVENTION

A first aspect of the invention is a method and apparatus for plating awafer that is particularly useful in improving the plating rate. Thisaspect of the invention comprises the technique of immersing a wafer ina bath of plating fluid and continuously directing fresh plating fluidtowards the surface of the wafer. The directing of plating fluid towardsthe surface of the wafer increases the ion concentration gradientbetween the cathode-contacted wafer and the anode. The current betweenthe anode and the cathode is proportional to the ion concentrationgradient at the surface of the wafer. The plating rate is alsoproportional to the current. Accordingly, increasing the ionconcentration gradient by continuously directing plating fluid towardsthe surface of the wafer, increases the current, and therefore increasesthe plating rate. Thus, a relatively high plating rate can be achievedby directing plating fluids towards the wafer, while the wafer isimmersed in a bath of plating fluid.

A second aspect of the invention is a method and apparatus for plating awafer that is particularly useful in plating high aspect ratio viaholes. This aspect of the invention comprises the technique of immersinga wafer with the side to be plated facing up in a bath of plating fluid.By immersing a wafer in a bath of plating fluid, any pockets of air orgas formed within via holes rise due to buoyancy and therefore, move outof the via hole. Accordingly, the absence of trapped pockets of air orgas within via holes allows the plating ions to better adhere to thewalls of via holes without hindrance if, otherwise, the trapped air orgas were present.

A third aspect of the invention is an apparatus and method for plating awafer that is particularly useful in improving the uniformity of theplating deposition across the surface of a wafer. This aspect of theinvention comprises continuously effecting random plating fluid flow inthe horizontal directions (i.e. x-y directions) within a bath of platingfluid. The random horizontal fluid flow in a plating fluid bath reducesthe occurrences of relatively long horizontal fluid flow path. Longhorizontal fluid flow path forms uneven plating of the surface of awafer. Accordingly, effecting random horizontal plating fluid flow helpsin improving the uniformity of the plating thickness across the surfaceof the wafer.

A fourth aspect of the invention is an apparatus and method for platinga wafer that is particularly useful in improving the uniformity of theplating deposition across the surface of a wafer. This aspect of theinvention comprises configuring the electrostatic field lines betweenthe anode and the cathode so that a more uniform current distributionacross the surface of the wafer is formed. A substantially uniformplating current across the surface of the wafer provides for asubstantially uniform thickness of the plating deposition across thesurface of the wafer. In the preferred implementations, theelectrostatic fields can be configured by providing a selectively shapedanode and/or cathode, by providing an electrostatic shield between theanode and the cathode, and/or providing an electrical conductor betweenthe anode and cathode that can alter the electrostatic field in responseto a control voltage.

A fifth aspect of the invention is an apparatus and method for plating awafer that is particularly useful in improving the uniformity of theplating deposition across the surface of a wafer, improving the platingrate, and minimizing cathode contact damage to the wafer. This aspect ofthe invention comprises providing an electrically conductive liquid inorder to effectuate the cathode contact to the surface of the wafer. Inthe preferred embodiment, the conductive liquid comprises a mixture ofsulfuric acid and de-ionized water. Preferably, the conductive liquid issupported by an annular channel configured so that the conductive liquidmakes contact to the perimeter region (e.g. exclusion zone) of the wafersurface. Because the conductive liquid provides a continuous and uniformcontact to the wafer, the uniformity of the plating deposition acrossthe surface of the wafer is improved. Because the conductive liquidmakes a continuous contact, a large surface contact area is achieved forproviding increased current capacity which improves the plating rate.Because the cathode connection to the wafer is accomplished by a liquid,this minimizes mechanical damage to the wafer.

A sixth aspect of the invention is an apparatus and method for plating awafer that is particularly useful in preventing acidic damage to thecopper seed layer of the wafer during the initial stage of forming theplating fluid bath. This aspect of the invention comprises providing asecondary anode near the surface of the wafer that is energized with apositive voltage. The positive voltage activates the plating fluid thatis initially introduced into the bath, and prevents the acidicproperties of the plating fluid from damaging the copper seed layer ofthe wafer. Once the primary anode is immersed, the positive voltage onthe secondary anode is removed.

A seventh aspect of the invention is an apparatus and method for platinga wafer that is particularly useful in improving the uniformity of theplating deposition across the surface of the wafer when the wafer isinitially being plated. When the wafer is initially being plated, thesurface resistance of the wafer is high due to the high resistiveproperties of the seed layer (e.g. copper seed layer). As a result, moreof the plating is deposited where the cathode makes contact to the wafer(e.g. at the perimeter of the wafer). This aspect of the inventioncomprises providing a secondary cathode situated near the cathodecontact of the wafer to reduce the plating rate near the cathode contactin response to a control voltage that is more negative than the cathode.The more negative voltage on the secondary cathode diverts plating ionsthat would otherwise be deposited near the cathode contact. The controlvoltage is selected to improve the uniformity of the plating depositionacross the surface of the wafer.

Additional aspects of the invention include (1) an apparatus and methodfor initial loading of a wafer; (2) an apparatus and method for waferalignment and final loading; (3) an apparatus and method for supportinga wafer; (4) an apparatus and method for cathode alignment; (5) anapparatus and method for cathode contacting a wafer; (6) an apparatusand method of draining the plating fluid bath; (7) an apparatus andmethod of drying an anode; (8) an apparatus and method of rinsing awafer after plating; (9) an apparatus and method of drying a wafer; (10)an apparatus and method of draining fluids from the plating apparatus;(11) an apparatus and method of controlling and disposing of fumes; (12)an apparatus and method of unloading a wafer; and (13) an apparatus andmethod of cleaning the plating apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a simplified diagram of a plating apparatus that isused to illustrate an aspect of the fluid dynamics of the plating methodof the invention;

FIG. 2 illustrates another simplified diagram of a plating apparatusthat is used to illustrate an aspect of the fluid dynamics of theplating method of the invention;

FIG. 3 illustrates a graph of the concentration of the plating ions inthe plating fluid as it varies with the depth of the plating fluid bath;

FIG. 4 illustrates a simplified diagram of a plating apparatus that isused to illustrate another aspect of the fluid dynamics of the platingmethod of the invention;

FIGS. 5A-5D illustrate simplified diagrams of plating apparatus used toillustrate an aspect of the plating method in accordance with theinvention;

FIG. 6 illustrates a top view of a wafer used to illustrate anotheraspect of the electrostatics of the plating method in accordance withthe invention.

FIG. 7 illustrates a cross-sectional view of an exemplary platingapparatus in a plating position in accordance with the invention;

FIG. 8 illustrates a cross-sectional view of an exemplary platingapparatus in a wafer insertion position in accordance with theinvention;

FIG. 9 illustrates a close-up cross-sectional view of a wafer mountingassembly in accordance with the invention, with a wafer supported by awafer loader above the wafer mounting assembly;

FIG. 10 illustrates a top view of the wafer mounting assembly inaccordance with the invention;

FIG. 11 illustrates a close-up cross-sectional view of a wafer mountingassembly in accordance with the invention, with a wafer supported bywafer supporting posts above the wafer loader and the wafer mountingassembly;

FIG. 12 illustrates a close-up cross-sectional view of a wafer mountingassembly in accordance with the invention, with a wafer in an alignmentzone;

FIGS. 13A-C illustrate blow-up views of a portion of the wafer mountingassembly, with the wafer undergoing alignment procedure in accordancewith the invention;

FIG. 14 illustrates a close-up cross-sectional view of a wafer mountingassembly in accordance with the invention, with a wafer in a finalloading position;

FIG. 15 illustrates a top view of a cylinder/distribution ring assemblyin accordance with the invention;

FIG. 16 illustrates a top view of the plating apparatus in accordancewith the invention;

FIGS. 17A-B illustrate a cross-sectional view and blow up view of thecylinder/distribution ring assembly in mating relationship with thewafer mounting assembly in accordance with the invention;

FIG. 18 illustrates a blow-up cross-sectional view of a portion of thewafer mounting assembly having a conductive fluid channel and feed/drainline in accordance with the invention;

FIG. 19 illustrates a close-up cross-sectional view of a rotary assemblyin accordance with the invention;

FIGS. 20A-B illustrate side and top views of an exemplary insolubleanode in accordance with the invention;

FIGS. 21A-B illustrate top and cross-sectional views of a soluble anodeassembly in an angled-up configuration in accordance with the invention;

FIGS. 22A-B illustrate top and cross-sectional views of a soluble anodeassembly in an angled-down configuration in accordance with theinvention;

FIGS. 23A-B illustrate top and cross-sectional views of a soluble anodeassembly in a flat configuration in accordance with the invention;

FIG. 23C illustrates a cross-sectional view of a flat anode assemblywith upper and lower electrostatic shields;

FIG. 24 illustrates a cross-sectional view of a portion of the platingapparatus that includes an apparatus for providing a cathode voltage toa cathode ring;

FIG. 25 illustrates a cross-sectional view of the plating apparatus in afluid draining position in accordance with the invention;

FIG. 26 illustrates a close-up cross-sectional view of thecylinder/distribution ring and the wafer mounting assembly in a waferrinsing configuration in accordance with the invention;

FIG. 27 illustrates a top view of a sump in accordance with theinvention; and

FIGS. 28A-B illustrate top and side cross-sectional views of a sumpvalve in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Method of Plating Wafers, Substrates or Other Articles

One aspect of the invention is a unique method of plating wafers,substrates or other articles. The objectives achieved by the platingmethod of the invention includes providing a relatively fast platingrate, providing a substantially uniform plating deposition across thesurface of a wafer, and providing improved plating of high aspect ratiovia holes. These objectives are achieved by uniquely implementing thefluid dynamics and the electrostatics of the plating method andapparatus. Although the plating of a wafer is used herein to illustratethe plating method and apparatus of the invention, it shall beunderstood that other articles, such as ceramic substrates, can beplated with the method and apparatus of the invention.

A. The Fluid Dynamics of the Plating Process of the Invention

The plating method of the invention provides for a unique implementationof the fluid dynamics of the plating process in order to achieve arelatively fast plating rate, a substantially uniform plating depositionon the surface of the wafer, and improved plating of high aspect ratiovia holes. One aspect of the fluid dynamics of the plating process isforcibly directing fresh plating fluid toward the surface of the waferwhile the wafer is immersed in a bath of plating fluid. This aspectimproves the plating rate. Another aspect of the fluid dynamics of theplating process is continuously effecting random plating fluid flow inthe horizontal directions (i.e. x-y directions) within a bath of platingfluid to improve the uniformity of the plating deposition across thesurface of the wafer. Yet another aspect of the fluid dynamics of theplating process is positioning a wafer near the bottom of a bath ofplating fluid to improve the plating of high aspect ratio via holes.

FIG. 1 depicts a simplified diagram of a plating apparatus 100 that isused to illustrate an aspect of the fluid dynamics of the plating methodof the invention. This aspect of the plating method of the inventionprovides for a relatively fast plating rate of the surface of a wafer bycontinuously replenishing the plating ions at the surface of the wafer.This is preferably performed by immersing a wafer 102 in a bath ofplating fluid 104 contained by a suitable container 106, andcontinuously directing fresh plating fluid 108 towards the wafer. Bycontinuously directing fresh plating fluid towards the surface of thewafer 102, a high concentration of the plating ions forms near thesurface of the wafer. The continuous high concentration of plating ionsnear the surface of the wafer helps in replenishing the ions near thesurface of the wafer, that are continuously being depleted from theplating fluid 104 due to the plating of the wafer 102. In theembodiment, a plurality of discrete nozzles 110 are employed to direct aplurality of streams of plating fluid towards the surface of the wafer102.

FIG. 2 depicts a simplified diagram of another plating apparatus 100′that is used to illustrate an aspect of the fluid dynamics of theplating method of the invention. The plating apparatus 100′ is similarto plating apparatus 100, and the same elements have the same referencenumbers to identify them. The plating apparatus 100′ differs fromapparatus 100 in that it includes a distribution element 110 for forminga plating fluid flow 108′ that cascades down the wall of the container106 towards the surface of the wafer 102. The distribution element 110includes an intake cavity 111 formed between the inside wall of thecontainer 106 and the distribution element 110. Plating fluid is fedinto the intake cavity 111, and thereafter, the plating fluid 108′cascades parallel to the container wall down to the wafer 102. Theplating apparatus 100′ may include a curved element 112 for directingthe cascading plating fluid towards the wafer 102. The advantage of thisembodiment is that the fluid flow towards the surface of the wafer 102does not directly impinge the surface of the wafer 102, and provides amore controlled flow towards the wafer 102.

FIG. 3 depicts a graph of the concentration of the plating ions in theplating fluid as it varies with the depth of the plating fluid bath. Thehorizontal axis of the graph represents the distance from the surface ofthe wafer and the vertical axis represents the concentration of theplating ions. As previously discussed, forcibly directing fresh platingfluid onto the surface of the wafer produces a higher concentration ofplating ions just above the surface of the wafer. Consequently, as thegraph illustrates, the concentration gradient dC/dZ of the plating ionsnear the surface of the wafer is substantially increased.

By increasing the flow rate of the fresh plating fluid impinging thesurface of the wafer, the plating ion concentration gradient dC/dZincreases. The ion electrical current that is formed within the platingfluid bath when a potential is applied between an anode situated nearthe top of and within the fluid bath and the cathode connected to thesurface of the wafer is proportional to the concentration gradient dC/dZnear the surface of the wafer. Thus, by increasing the ion concentrationgradient dC/dZ by forcibly directing fresh plating fluid onto thesurface of the wafer, the electric current propagating within the fluidbath increases, which, in turn, increases the plating rate. Thus, a highplating rate can be achieved by the plating method of the invention byforcibly directing fresh plating fluid onto the surface of the wafer.

FIG. 4 depicts a simplified diagram of a plating apparatus 150 that isused to illustrate another aspect of the fluid dynamics of the platingmethod of the invention. This aspect of the plating method of theinvention improves the uniformity of the plating deposition across thesurface of the wafer by continuously effecting random plating fluid flowin the horizontal directions (i.e. x-y directions) within a bath ofplating fluid. This is preferably performed by immersing a wafer 152 ina bath of plating fluid 154 contained by a suitable container 156, andrandomly stirring the fluid bath 154 with one or more paddles 158 beingrotated about a vertical axis. The rotation of the paddles 158 may beperformed by a motor 160 being controlled by a processor 162 to rotatein a random manner. The processor 162 can be a microprocessor, computeror other suitable means.

The objective of continuously effecting random plating fluid flow in thehorizontal directions (i.e. x-y direction) within a bath of platingfluid is to eliminate relatively long paths of plating fluid flow in thehorizontal direction (i.e. x-y direction). The problem with longhorizontal fluid paths is that it produces gradients in the platingdeposition across the surface of the wafer. Specifically, at a beginningof such a horizontal fluid path, the plating ion concentration is high.As a result, a high percentage of the plating ions are deposited on thesurface of the wafer at the beginning of a horizontal fluid path. As thehorizontal fluid path proceeds, the plating ions are continuouslydepleted. Thus, from the beginning towards the end of a horizontal fluidpath, the plating ions deposited on the surface of the wafer graduallydecreases. This leads to a non-uniformity of the plating depositionacross the surface of the wafer. By stirring the plating fluid bath in arandom manner in the horizontal direction, the lengths of horizontalfluid paths are substantially shortened, thus resulting in animprovement in the uniformity of the plating deposition across thesurface of the wafer.

The plating method of the invention is particularly useful in providingimproved step coverage of via holes that are typically formed throughthin film layers situated on the surface of a wafer. The reason thepreferred implementation of the plating method of the invention providesimproved step coverage of via holes is that the wafer 102 is immersed ina bath of plating fluid. As a result, any pockets of air or gas formedwithin via holes rise due to buoyancy and therefore, move out of viaholes. Accordingly, the absence of trapped pockets of air or gas withinvia holes, allows the plating ions to better adhere to the walls of viaholes without hindrance if, otherwise, the trapped air or gas werepresent.

B. The Electrostatics of the Plating Method of the Invention

The plating method of the invention provides for a unique implementationof the electrostatics of the plating process in order to assist inproviding substantially uniform plating across the surface of the waferand providing an improved plating rate. One aspect of the electrostaticsof the plating process of the invention comprises configuring theelectrostatic field lines between the anode and the cathode in a mannerthat the current distribution across the surface of the wafer issubstantially uniform during the plating process. The substantiallyuniform current distribution across the surface of the wafer helps inproviding uniform plating of the surface of the wafer. Another aspect ofthe electrostatics of the plating process of the invention is toconfigure the cathode contact to the wafer surface to provide arelatively large contact surface to improve the current capacity of theplating (without occupying the useful surface area of the wafer), and tominimize damage to the wafer surface due to the contact.

FIGS. 5A-5D depict simplified diagrams of plating apparatus (200, 214,224, 230) used to illustrate the electrostatic aspect of the platingmethod related to configuring the electrostatic field lines between theanode and the cathode to provide a more uniform current distributionacross the surface of the wafer. This is accomplished by configuring theanode or assembly and/or the cathode or cathode assembly in a mannerthat the effective resistances of current paths outlined by respectiveelectrostatic field lines between the anode and the cathode aresubstantially the same.

Referring initially to FIG. 5A, it depicts a simplified diagram of aplating apparatus 200 that includes a container 202 supporting a bath ofplating fluid 204, and a wafer 206 preferably disposed on the bottom ofthe container 202. This configuration applies to the other platingapparatus 214, 224 and 230. A continuous cathode contact or a pluralityof cathode contacts 208 are in contact with the surface of the wafer 206preferably around the perimeter of the wafer. The plating apparatus 200also includes an anode 210 situated within the plating fluid bath 204,above the wafer 206.

In operation, when a voltage potential difference is formed between theanode 210 and the cathode 208, an electrostatic field is formed betweenthe anode and the cathode. As customary, the electrostatic field can berepresented as a plurality of field lines 212 emanating from the anode210 and terminating at the cathode 208 (for simplicity, five field lines212 a-e are shown in FIG. 5A). In addition to the electrostatic fieldforming between the anode and the cathode in response to a voltagepotential difference between the anode and the cathode, current flowoccurs between the cathode and the anode that substantially parallel thepaths of the field lines 212. The amount of current flow that parallelsthe path of a particular field line is inversely proportional to theeffective resistance between the anode 210 and the cathode 208 alongthat path. The sources of the resistance are the plating fluid 204 aswell as the surface of the wafer 206. In order for the currentdistribution across the surface, of the wafer 206 to be substantiallyuniform, the anode 210 and/or cathode 208 is/are configured in a mannerthat the effective resistances of current paths outlined by respectiveelectrostatic field lines 212 are substantially the same.

One preferred manner of substantially equalizing the resistances of thepaths outlined by the field lines, shown in FIG. 5A, is to provide ananode 210 that is curved in a concave upward manner with respect to thewafer 206. With this curved anode 210, the field lines 212 a and 212 eemanating from the anode that are laterally closer and follow a directpath to the cathode 208 are lengthen (assuming the anode was previouslystraight for illustration purposes) to increase their resistances.Whereas the field lines 212 b-d that are laterally farther away and/orfollow an indirect path to the cathode 208 via the surface of the wafer206 are shortened (assuming the anode was previously straight forillustration purposes) to lower their resistance. In this manner, theresistances of the field line paths are substantially equalized, whichresults in a substantially uniform current distribution across thesurface of the wafer 206. It is this substantially uniform currentdistribution across the surface of the wafer 206 that helps in providingsubstantially uniform plating of the surface of the wafer.

Another preferred manner of substantially equalizing the resistance ofcurrent paths outlined by the field lines, shown in FIG. 5B, is toprovide an anode 216 and a shield 218 situated between the anode 216 andthe wafer 206, and preferably attached to the anode 216. In a preferredembodiment, the shield 218 includes a portion 220 that shields thesections of the anode 216 that are closer to the cathode 208, whileleaving a central portion of the anode exposed. In addition, the shieldincludes an additional portion 222 that extends downward a specifieddistance from the anode 216 at the perimeter of its exposed centralsection. This configuration substantially equalizes the resistances ofthe field line paths, which results in a substantially uniform currentdistribution across the surface of the wafer 206, and thereby, improvethe uniformity of the plating of the wafer surface.

Although in the preferred embodiment the cathode contacts the perimeterof the wafer 206, it shall be understood that the principle of themethod of the invention shall not be limited to such configuration. Forinstance, if the cathode contacts were at the center of the wafer,although not a preferred placement of the cathode, the anode can beconfigured also to provide a substantially uniform current distributionacross the surface of the wafer by equalizing the resistances of fieldline paths. For instance, if the cathode contact were positioned at thecenter of the wafer 206, as in apparatus 224 shown in FIG. 5C, an anode228 can be configured into a concave downward shape with respect to thewafer in order to substantially equalize the resistances of the fieldline paths. Alternatively, an anode 216 including a shield 234, as inapparatus 230 shown in FIG. 5D, can be configured in order tosubstantially equalize the resistances of the field line paths.

FIG. 6 illustrates a top view of a wafer 250 used to illustrate anotheraspect of the electrostatics of the plating method in accordance withthe invention. This aspect of the invention improves the uniformity ofthe plating of the surface of the wafer, and also improves the platingrate. Specifically, this aspect of the electrostatics of the platingmethod comprises the step of providing a continuous and substantiallyuniform cathode contact along and within the perimeter area 252 of thewafer 250. This perimeter area is typically 3 millimeters wide and isreferred to in the art as the “exclusion zone.”

In the preferred embodiment, the cathode contact comprises anelectrical-conductive fluid, such as a mixture of sulfuric acid andde-ionized (DI) water. The conductive fluid is significantlyadvantageous because it provides a uniform contact along and within theexclusion zone (i.e. the contact has a uniform resistance along andwithin the exclusion zone). Because of the continuity of the cathodecontact provided by the conductive fluid, a more uniform platingdeposition and higher currents for increasing the plating rate results.Alternatively, a mechanical contact comprising a plurality of equallyspaced contacts can be provided along and within the exclusion zone toeffectuate the cathode contact to the wafer.

II. Apparatus and Corresponding Methods Involved in Plating a Wafer

A. Introduction and Overview

In this section of the specification, a plating apparatus is describedthat is a preferred physical implementation for achieving the fluiddynamic and electrostatic aspects of the plating method of theinvention. Specifically, with regard to the fluid dynamic aspects of theplating method, the plating apparatus of the invention (1) forciblydirects fresh plating fluid toward the surface of the wafer while thewafer is immersed in a bath of plating fluid to improve the platingrate; (2) continuously effects random plating fluid flow in thehorizontal direction (i.e. x-y direction) within the plating fluid bathto improve the uniformity of the plating deposition across the surfaceof the wafer, and (3) positions the wafer near the bottom of the platingfluid bath to improve the plating of high aspect ratio via holes. Withregard to the electrostatic aspects of the plating method, the platingapparatus of the invention (1) configures the electrostatic field linesbetween the anode and the cathode in a manner that the currentdistribution across the surface of the wafer is substantially uniformduring the plating process; and (2) configures the cathode contact tothe wafer surface to provide a relatively large contact surface toimprove the current capacity of the plating (without occupying theuseful surface area of the wafer) and to also provide a substantiallyuniform plating deposition across the surface of the water.

FIG. 7 illustrates a cross-sectional view of an exemplary platingapparatus 300 in accordance with the invention. The plating apparatus300 of the invention comprises three principle assemblies relating tothe plating process. These assemblies include a wafer mounting assembly302, a cylinder/distribution ring assembly 304, and an anode assembly306. During the plating process, the cylinder/distribution ring assembly304 makes a fluid seal contact with the wafer mounting assembly 302 toform a plating solution (fluid) bath. A wafer 308 is mounted on top ofthe wafer mounting assembly 302 and is situated at the bottom of theplating fluid bath to improve the plating of via holes, as previouslydiscussed. The cylinder/distribution ring assembly 304 includes anannular slot for directing fresh plating fluid down onto the surface ofthe wafer 308 to improve the plating rate of the plating process, aspreviously discussed.

The anode assembly 306 is situated within the cylinder/distribution ringassembly 304 during the plating process and is immersed within theplating fluid bath. The anode assembly 306 includes paddles 510 whichare rotated about a vertical axis in a manner to effectuate random fluidflow in a horizontal direction. This improves the uniformity of theplating deposition formed on the surface of the wafer 308. The anodeassembly 306 can be configured or altered to provide for substantiallyuniform current distribution across the surface of the wafer, aspreviously discussed. Finally, the cylinder/distribution ring assembly304 includes a cathode structure that makes electrical contact with theexclusion zone of the wafer during the plating process, as previouslydiscussed. The three principle assemblies are discussed in more detailin the sections to follow.

In addition to the three principle assemblies and their correspondingplating method, the wafer apparatus 300 also includes other apparatusand method associated with the plating process. These include (1) anapparatus and method for initial loading of a wafer; (2) an apparatusand method for wafer alignment and final loading; (3) an apparatus andmethod for supporting a wafer; (4) an apparatus and method for cathodealignment; (5) an apparatus and method for cathode contacting a wafer;(6) an apparatus and method of draining the plating fluid bath; (7) anapparatus and method of drying an anode; (8) an apparatus and method ofrinsing a wafer after plating; (9) an apparatus and method of drying awafer; (10) an apparatus and method of draining fluids from the platingapparatus; (11) an apparatus and method of controlling and disposing offumes; (12) an apparatus and method of unloading a wafer; and (13) anapparatus and method of cleaning the plating apparatus. The followingdetailed discussion of the plating apparatus will follow a chronologicalorder beginning with the initial loading of the wafer into the platingapparatus and ending with the unloading of the wafer after completion ofthe plating process.

B. Apparatus and Method for Initial Loading of a Wafer into an AlignmentZone

FIG. 8 illustrates a cross-sectional view of the exemplary platingapparatus 300 of the invention immediately prior to the insertion of awafer 308 for initial loading into the plating apparatus. At this stage,the cylinder/distribution ring assembly 304 is preferably positioned atits full raised position, leaving a sufficient clearance 311 between thecylinder/distribution ring assembly 304 and the wafer-mounting assembly302 to insert a wafer therein. As will be discussed in more detail, thecylinder/distribution ring assembly 304 can be selectively raised orlowered to a desired position. At the moment, three vertical positionsfor the cylinder/distribution ring assembly 304 are contemplated: (1)the full raised position shown in FIG. 8 for insertion and removal ofthe wafer 308 to and from the plating apparatus; (2) in the full lowerposition where the bottom of the cylinder/distribution ring makescontact with the wafer mounting assembly 302 as shown in FIG. 7; and (3)in a fluid draining position as shown in FIG. 25. However, it shall beunderstood that any other position between the full raised and lowerpositions are available.

FIG. 9 illustrates a close-up cross-sectional view of the wafer mountingassembly 302 with a wafer 308 positioned above the wafer-mountingassembly 302, and supported by a wafer loader 312. The wafer mountingassembly 302 includes a wafer mounting base 314 mounted on top of ahousing 316, by suitable means such as screws 317. The housing 316encloses an inner cavity 318 that includes at least a portion of a liftpost assembly 320, among other components. The housing 316 protects thelift post assembly 320 and other components from the solutions involvedin the plating process.

The lift post assembly 320 comprises at least three elongated wafersupporting posts 322 (two shown in FIG. 9) situated coaxially withinrespective vertical channels formed through the wafer-mounting base 314.One or more O-rings 315 may be placed coaxially around each of thesupporting posts 322 to prevent leakage of plating, rinsing and/or otherfluids through the vertical channels of the wafer mounting base 314. Thewafer supporting posts 322 are mounted on a movable mounting plate 324situated within the housing 316. In the preferred embodiment, each ofthe wafer supporting posts 322 includes a bottom narrower portion 326that extends into and below a hole formed through the movable mountingplate 324. The portion of the wafer supporting posts 322 above the lowernarrower portion 326 is wider and sits on top of the horizontal mountingplate 324. The movable mounting plate 324 is securely coupled to a leadscrew 328 by way of an collet coupling 330 and adapter 332 mounted ontop of the movable mounting plate 324.

The lead screw 328 extends downward from the collate coupling 330through a clearance hole in the movable mounting plate 324 to anelectric motor 334. The lead screw 328 is coupled to an internalrotating acme nut (not shown) driven by the electric motor 334 whichcauses axial movement of the lead screw 328. The motor 334 is mounted toa stationary motor mounting plate 336 that is securely coupled to lowerends of at least three guide posts 338 (one shown in FIG. 9). The upperends of the guideposts 338 are securely connected to a horizontalmounting plate 340 secured to the underside of the wafer-mounting base314. The guideposts 338 extend through holes in the movable mountingplate 324 that are lined with respective bushings 342. The guide posts338 assist in the vertical alignment and retrain lateral and rotationalmovement of the movable mounting plate 324. The wafer supporting posts322 extend through holes in the horizontal mounting plate 340 that arealso lined with respective bushings 344.

Each of the wafer supporting posts 322 includes a duct 346 extendingcoaxial therein from the top of the posts 322 to its bottom portion 326.The bottom portion 326 of each of the wafer supporting posts 322includes an inner threaded wall for receiving therein a fitting 348 of avacuum hose 350. The vacuum hose 350 is coupled to a pump (not shown)for forming a vacuum at the top of the wafer supporting posts 322.Situated on top of each wafer supporting post 322 is a vacuum cup 352 ina bellows configuration and having a channel therein in fluidcommunication with duct 346. Also situated on top of each of the wafersupporting posts 322 is a mechanical stop 354.

FIG. 10 illustrates a top view of the wafer mounting assembly 302. Thethree wafer supporting posts 322 with respective vacuum cups 352 andmechanical stops 354 are spaced annularly around a fluid bed 356 withsubstantially the same angular distance from each other. Since there arethree wafer-supporting posts 322 in the preferred embodiment, each ofthem are separated by 120°. Although the preferred embodiment includesthree wafer supporting posts 322, it shall be understood that more canbe incorporated into the wafer mounting assembly 302. The purpose of thefluid cavity bed 356 will be explained in a subsequent section of thespecification.

Referring again to FIG. 9, the method of the invention for initiallyloading a wafer 308 into the plating apparatus 300 will now bedescribed. The first step in the initial wafer loading method is totransport the wafer 308 from outside of the plating apparatus 300 to theclearance area 311 above and generally aligned with the wafer mountingassembly 302. This can be performed by any suitable wafer loader 312,such as a movable platform, robotic arm or any device that can positionthe wafer 308 above and approximately aligned with the wafer mountingassembly 302, and in a substantially horizontal orientation. FIG. 9depicts the condition of the wafer mounting assembly 302 at the end ofthis step, with the wafer 308 and wafer loader 312 situated above thewafer mounting assembly 302.

Referring to FIG. 11, a subsequent step in the initial wafer loadingmethod of the invention is to raise the wafer supporting posts 322 tomake vacuum contact with the underside of the wafer 308 and lift thewafer off the wafer loader 312. This is performed by actuating theelectric motor 334 to cause the lead screw 328 to move in an axiallyupward direction. The upward movement of the lead screw 328 causes themovable horizontal mounting plate 324 to rise along with the wafersupporting posts 322. When the top of the wafer supporting pins 322 isnear the underside of the wafer 308, negative pressure is introducedthrough the hose 350 to form a vacuum contact of the wafer 308 to thetop of the supporting pins 322. The vacuum cup 352 compresses due to thevacuum allowing the wafer 308 to sit on the mechanical stops 354. Aftermaking vacuum contact with the underside of the wafer 308, thesupporting posts 322 continue to rise to lift the wafer 308 off of thewafer loader 312. The wafer loader 312 is now removed.

Referring to FIG. 12, a subsequent step in the initial wafer loadingmethod of the invention is to lower the wafer supporting pins 322 toposition the wafer 308 within an alignment zone. The alignment zone is aregion laterally adjacent to the tapered end of alignment pins 358. Thispositioning of the wafer 308 is performed by actuating the electricmotor 334 to move the lead screw 328 in an axially downward direction.The downward movement of the lead screw 328 causes the movable mountingplate 324 and wafer supporting posts 322 to lower the wafer 308 until itis situated in the alignment zone. The movement of the wafer 308 intothe alignment zone completes the method of initially loading the wafer.

Although the preferred implementation of the lift post assembly 320includes an electric motor 334 for causing the vertical movement of thewafer supporting posts 322, it shall be understood that there are manyother ways of vertically moving the posts 322. For example, one such wayis to use a pneumatic actuator, instead of an electric motor.

C. Apparatus and Method for Wafer Alignment and Final Loading

In the previous method of initially loading the wafer 308 into analignment zone, the wafer loader 312 positions the wafer 308 generallyabove the wafer final loading region. However, it is difficult toposition the wafer 308 over the final loading region to the desiredtolerance. As previously discussed in Section I-B, it is an object ofthe invention to provide a cathode that makes contact to the surface ofthe wafer 308 within the exclusion zone. The exclusion zone is theconcentric ring area adjacent the perimeter of the wafer 308 and istypically around 3 millimeters wide. Therefore, because of the tighttolerance required for positioning the wafer 308 into its final loadingposition, there is a need for an apparatus and method for waferalignment and final loading.

Referring to FIG. 12, a wafer alignment apparatus in accordance with theinvention comprises three or more wafer alignment pins 358 coaxiallyoriented within vertical channels formed through the wafer mounting base314. One or more O-rings 359 may be situated coaxially around each ofthe wafer alignment pins 358 within the corresponding vertical channelto prevent leakage of plating, rinsing and/or other fluids therethrough.The lower end of the wafer alignment pins 358 are mounted to horizontalmounting plate 340. The upper end of each of the wafer alignment pins istapered. The tapered end of each of the wafer alignment pins 358 and astraight upper portion thereof are situated above the wafer mountingbase 314. As seen in FIG. 10, the wafer alignment pins 358 are annularlyspaced around the wafer final loading position 308, preferablycoincident with the wafer supporting posts 322. It shall be understoodthat more than three wafer alignment pins 358 may be provided.

FIG. 13A illustrates a blow-up view of the wafer 308 situated in thealignment zone immediately after undergoing the initial loading methoddiscussed above. At this position, the wafer supporting post 322 ismaking vacuum contact with the underside of the wafer 308 via the vacuumcup 352, and the wafer 308 is seated on the mechanical stop 354. Aspreviously defined, the alignment zone is a region laterally adjacent tothe tapered end of alignment pins 358. To exemplify the alignment methodof the invention, the wafer 308 is shown slightly misaligned. In itsfinal loading position, the edge of the wafer 308 lies approximatelyadjacent to the vertical surface of the alignment pin 358. Accordingly,the wafer 308 shown in FIG. 13A is misaligned by a distance of ΔL.

As illustrated in FIGS. 13A-B, a first step in the method for waferalignment and final loading is to remove the vacuum contact of the wafersupporting posts 322 to the underside of the wafer 308. Then, the wafersupporting posts 322 are lowered by actuating the motor 334 to positionthe top of the posts 322 slightly above the final loading position. Thelowering of the wafer supporting posts 322 causes the wafer 308 to drop.The wafer 308 then self-aligns by contacting and sliding down thetapered end of the alignment pin 358. Thus, at the end of this step, thewafer 308 is positioned approximately below the tapered end of thealignment pin 358, and is horizontally aligned with and positionedslightly above the final loading position.

As illustrated in FIGS. 13B-C, a subsequent step in the method for waferalignment and final loading is to re-engage the vacuum contact of thetop of the wafer supporting posts 322 to the underside of the wafer 308.Then, the motor 334 is actuated to lower the wafer supporting posts 322so that the edge of the wafer 308 is disposed on the wafer mounting base314. The wafer 308 is now in its final loading position. At the finalloading position, the edge of the wafer 308 lies approximately adjacentto the three alignment pins 358 (See FIG. 10). Although alignment pins358 are used to cause the wafer 308 to self align, it shall beunderstood that other structures having an inclined surface such as thetapered end of the alignment pins 358 can also be used in accordancewith the invention.

D. Apparatus and Method for Supporting the Wafer

As previously discussed in Section I-A of the specification, one aspectof the fluid dynamics of the invention is to position the wafer near thebottom of a bath of plating fluid. The bath, however, may comprise alarge volume of plating fluid. Because the wafer is situated near thebottom of the bath, the large volume of plating fluid exerts substantialhydrostatic pressure on the wafer. If the perimeter of the wafer weredisposed on a mechanical surface (e.g. an annular pad support), thehydrostatic pressure may cause the wafer to crack and/or deform. Inaddition, the cracking and/or warping of the wafer may cause platingfluid to creep under the wafer and contaminate the wafer underside.Accordingly, there is a need for an apparatus and method for supportingthe wafer such that it will not flex because the hydrostatic pressure onboth side of the wafer is substantially equalized. This prevents thewafer from cracking and/or deforming.

FIG. 14 illustrates a cross-sectional view of the wafer mountingassembly 302 with the wafer 308 in its final loading position. The wafermounting base 314 includes a circular recess 356 that is approximatelyconcentric with the wafer 308 in its final loading position. The recess356 is preferably horizontal around its center region and inclinedelsewhere. The diameter of the recess 356 is slightly smaller than thediameter of the wafer 308. This allows the perimeter of the wafer 308 torest on the wafer mounting base 314. The majority of the wafer 308,except for the perimeter area supported by the wafer mounting base 314,is supported by a wafer supporting fluid that is situated within therecess 356. The wafer supporting fluid counteracts the pressure from theplating fluid bath, and prevents the wafer 308 from cracking and/ordeforming by evenly distributing the pressure and conforms to anysurface irregularities on the surface of the wafer. Therefore, the wafersupporting fluid provides a continuous counteracting hydrostatic force,even though the wafer is non-planar. In the preferred embodiment, thewafer supporting fluid comprises de-ionized (DI) water.

In the preferred implementation of the method for supporting the wafer,the wafer supporting fluid is introduced into the recess 356 prior tothe positioning of the wafer 308 into its final loading position. Whilethe wafer 308 is situated above the final loading position, wafersupporting fluid is introduced into the recess 356 by way of feed/draintube 360 situated within the housing 316 of the wafer mounting assembly302. The end of the feed/drain tube 360 includes a fitting 362 formating with a threaded hole in the wafer-mounting base 314. A small duct364 extends from the threaded hole to the recess 356, preferably nearits center. Once the recess 356 is filled with the wafer supportingfluid such that the fluid level is approximately at the top of the wafermounting base 314, the wafer 308 is lowered into its final loadingposition preferably in accordance with the method described in SectionII-C of the specification. Placing the wafer 308 onto its final loadingposition or pressure exerted by the plating or rinsing fluids may causedisplacement of the wafer supporting fluid on top of the wafer mountingbase 314. This is a spill over area.

Although in the preferred embodiment, the recess 356 has a horizontalcenter section and an inclined outer section, it shall be understoodthat other configurations for the recess 356 can be employed. Forexample, the recess 356 can have a horizontal bottom and vertical walls.In addition, the end of the feed/drain 360 need not be positioned at thecenter, and it is plausible also to have separate feed and drain linesfor the wafer supporting fluid. Furthermore, the spill over area neednot be at the top surface of the wafer-mounting base 314, but overflowducts may be incorporated into the wafer mounting assembly 302 to drainout any displaced fluid from the recess 356. These types ofmodifications are within the purview of one skilled in the relevant art.

E. Apparatus and Method for Cathode Alignment

Once the wafer 308 is in its final loading position as described inSection II-C and is supported by the wafer supporting fluid as describedin Section II-D, the next step in the overall plating process is toalign the cathode to the wafer for making contact therewith. As with thealignment of the wafer 308, the alignment of the cathode is alsocritical because of the small exclusion zone of the wafer surface towhich the cathode needs to make contact. Since the cathode is located atthe bottom of the cylinder/distribution ring assembly 304, lowering thecylinder/distribution ring assembly 304 for proper placement on thewafer mounting assembly 302 is also critical.

Referring back to FIG. 8, the cylinder/distribution ring assembly 304 ispreferably at its full raised position during the initial loading, finalloading, and wafer supporting fluid steps as described in Sections II-B,C and D. During the plating method as will be described in Section II-G,the cylinder/distribution ring assembly 304 is at its full loweredposition making a fluid seal contact with the wafer mounting assembly302. To vertically position the cylinder/distribution ring 304, theplating apparatus 300 includes a cylinder lift assembly 400 comprisingthree or more two-mode pneumatic cylinder assemblies 402 (one shown inFIG. 8) mounted on a top horizontal mounting plate 404 for lowering andraising the cylinder/distribution ring assembly 304; three correspondingmechanical couplings 406 (one shown in FIG. 8) for coupling thecylinder/distributing ring assembly 304 to the pneumatic cylinderassemblies 402; and a flexible boot 408 mechanically coupled to the topof cylinder/distribution ring assembly 304 and to the underside of thetop mounting plate 404 for allowing small horizontal (x-y direction)movement of the cylinder/distribution ring 304, while restrictingrotational movement thereof.

Referring to both FIGS. 8 and 15 (which is a top view of thecylinder/distribution ring assembly 304), the mechanical couplings 406of the cylinder/distribution ring assembly 304 each comprises aprojection 407 having a through-hole 409. In the preferred embodiment,the three couplings 406 are annularly spaced around the cylinder withsubstantially equal angles between each of the coupling 406 (i.e. theyare 120° apart from each other). The couplings 406 extend radiallyoutward from the cylinder wall 444. It shall be understood that thereare many ways to couple the cylinder/distribution ring 304 to thecylinder lift assembly 400, which are within the purview of one skilledin the art.

Referring to both FIGS. 8 and 16 (top view of the plating apparatus),each of the two-mode pneumatic assemblies 402 comprises a long-strokecylinder 410 and a short-stroke cylinder 412, operating in combination,to provide vertical movement of the cylinder/distribution ring assembly304 from its full raised position to its full lower position. Theshort-stroke cylinder 412 also independently lifts thecylinder/distribution ring assembly 304 off the wafer mounting assembly302 for allowing drainage of the plating fluid, as will be explained inmore detail in Section II-H (the short-stroke cylinder 412 does not playa role in the cathode alignment). The long and short stroke cylinders410 and 412 are mounted on a plate 414 that is supported above the topmounting plate 404 by a base 416. Preferably, three guideposts 418extend upward from the top mounting plate 404 through the base 416 andplate 414, and above the plate 414. The short-stroke cylinder 412includes a piston 420 mechanically coupled to the base 416. Thelong-stroke cylinder 410 also includes a piston 424 coupled to anextender 426 that extends through and below the top mounting plate 404.A resilient mechanism 425, such as a spring, is sandwiched between plate414 and mounting plate 404 The extender 426 extends through the hole 409of the coupling mechanism 406 and terminates with a shoulder 428. Theshoulder 428 supports the cylinder/distribution ring assembly 304 duringvertical movement thereof. The extender 426 also includes a resilientmechanism 427, such as a spring, and a mechanical stop 429 situatedimmediately above the cylinder coupling mechanism 406. In the preferredembodiment, there are three two-mode pneumatic cylinder assemblies 402that are equally spaced in an angular direction to coincide with themechanical couplings 406. It shall be understood that more than threecylinder assemblies can be employed.

Referring to only FIG. 8, the flexible boot 408 preferably comprises acentral portion 430 that is configured into a bellows, and upper andlower ends that are configured into top and bottom flanges 432 and 434.The top flange 432 is connected to the underside of the top mountingplate 404 by any suitable means, such as screws 436. The bottom flange434 is connected to the top rim of the cylinder/distribution ringassembly 304 also by suitable means, such as screws 438. The flexibleboot is preferably made out of a resilient sealing material, such asViton® material, which is compliant in the horizontal direction (x-ydirection), but restricted rotationally.

Referring to both FIGS. 7 and 8, when the cylinder/distribution ringassembly 304 is lowered to mate with the wafer mounting assembly 302,both the long-stroke cylinder 410 and short-stroke cylinder 412 areactuated to the cylinder/distribution ring assembly. The lowering of thecylinder/distribution ring assembly 304 continues until it mates withthe wafer mounting assembly 302. The long-stroke cylinder 410 continuesto lower even after the cylinder mates with the wafer mounting assembly302 to allow the cylinder/distribution ring 304 to self-align with thewafer mounting assembly 302. This further lowering of the extender 426causes the mechanical stop 429 to compress the spring 427 so that adownward biasing force is produced to firmly hold thecylinder/distribution ring assembly 304 against the wafer mountingassembly 302. Note that when the cylinder/distribution ring 304 is atits full lower position, the shoulder 428 of the extender 426 is spacedapart from the coupling mechanism 406.

FIGS. 17A-B illustrate a cross-sectional view and blow up view of thebottom of the cylinder/distribution ring assembly 304 in matingrelationship with the top of the wafer mounting assembly 304. At itslower end, the cylinder/distribution ring assembly 304 comprises acathode ring 440 mounted to a cathode ring mount 442 that is, in turn,mounted to the cylindrical wall 444. An O-ring 443 is positioned betweenthe cylinder wall 444 and the cathode ring mount 442 to prevent leakageof plating or rinsing fluid between these two structures. The cathodering mount 442 includes an upper inclined surface 446 and a lowervertical surface 448. The cathode ring mount 442 serves three functions:(1) it provides a structure to which the cathode ring 440 is mounted to;(2) its inclined surface 446 and vertical surface 448 direct the platingand rinsing fluid toward the wafer 308; and (3) it protects the cathodering 440 from exposure to the plating fluid. For the purpose of properlyaligning the cathode ring 440 to the wafer mounting assembly 304 toprovide the desired contacting of the cathode to the exclusion zone ofthe wafer 308, the cathode ring 440 includes an alignment groove 450having a surface that is similarly inclined with the tapered end of thealignment pins 358.

The method of properly aligning the cathode ring 440 over the wafermounting assembly 304 will now be described. When thecylinder/distribution ring 304 is lowered for mating with the wafermounting assembly 302, the cathode ring 304 may be slightly misalignedin the horizontal direction. Because of the misalignment, the alignmentgroove 450 makes contact with the tapered end of one of the alignmentpins 358 when the cylinder is lowered. The contacting of the alignmentgroove 450 and the alignment pin 358 will cause thecylinder/distribution ring assembly 304 to self-align. The flexible boot408 allows the cylinder/distribution ring assembly 302 to be compliantin the horizontal direction (x-y direction) to allow the assembly 302 toself-align with the alignment pins 358. Furthermore, since the shoulder428 supporting the cylinder/distribution ring assembly 304 is lowered afurther distance below the coupling mechanism 406, thecylinder/distribution ring assembly 304 self-aligns on its own accord.As shown in FIG. 17A, proper alignment and positioning of the cathodering 440 over the wafer mount assembly 302 occurs when the alignmentgroove 450 is substantially adjacent to the alignment pins 358, and anO-ring 445 of the cathode ring 440 makes fluid seal contact with thewafer mounting base 314.

Although the cylinder lift assembly 400 uses pneumatic cylinders tovertically move the cylinder/distribution ring assembly 302, it shall beunderstood that there are many other methods of performing the samefunction. For example, an electric motor, such as a stepper motor, canbe used in place of a pneumatic cylinder. In addition, the couplingbetween the cylinder, distribution ring assembly 304 and the pneumaticassembly 412 need not comprise a piston/extender/shoulder supporting thecoupling mechanism 406, but can be any technique for supporting thecylinder 304 during its vertical movement. Finally, the flexible boot408 need not be made of a resilient sealing material, such as Viton®material in a bellows configuration, but can comprise any structure thatis compliant in the horizontal direction (x-y direction), whilerestricted rotationally.

F. Apparatus and Method for Cathode Contacting a Wafer

Referring to FIG. 18, it illustrates the apparatus and methodology usedfor providing a cathode contact to the surface of the wafer 308. Aspreviously discussed, the exclusion zone is a three (3) millimeter widering-shaped surface area adjacent to the perimeter of the wafer 308. Itis this area to which the cathode needs to make contact. The remainingarea of the wafer surface is reserved for the plating deposition. Withinthe exclusion zone, the cathode of the invention makes contact to theouter 2 millimeter wide ring-shaped surface area of the exclusion zone.This area is defined herein as the “cathode contact area.” The remainingsurface area of the exclusion zone, i.e. a 1 millimeter wide ring-shapedsurface area 2 millimeters away from the perimeter of the wafer, isreserved to make a fluid seal to prevent leakage of plating fluid viathe perimeter of the wafer 308. This area is defined herein as the“fluid seal area.”

To establish this fluid seal, a fluid sealing element 454 is providedbetween the cathode ring 440 and the cathode ring mount 442, andincludes a lip seal ring 456 that makes a fluid seal contact with thewafer 308 at the “fluid seal area.” The lip seal ring 456 preventsplating fluid from leaking through pass the perimeter of the wafer 308.This protects the cathode ring 440 from exposure to the plating fluid,as well as the underside of the wafer 308. Note that the cathode ring440 does not make mechanical contact to the “cathode contact area” ofthe wafer. Instead, a channel 458 exists between the lip seal ring 456and the alignment groove 450 for receiving an electrically conductivefluid. The conductive fluid within the channel 458 provides theelectrical connection of the cathode ring 440 to the “cathode contactarea” of the wafer 308. A feed/drain 460 is provided to introduce theconductive fluid into the channel 458 prior to plating, and to drain theconductive fluid after plating. In the preferred embodiment, theconductive fluid comprises 5-10 percent sulfuric acid and the remainingis DI water.

The advantage of using a conductive fluid versus a mechanical contact inmaking the cathode connection to the wafer 308 is that the fluid contactdoes not typically damage the wafer, whereas a mechanical contact tendsto warp and/or deform the wafer. Another advantage of the fluid contactis that it provides a relatively large contact surface area since thecontact is continuous throughout the “cathode contact area.” Forexample, the two (2) millimeter wide cathode contact area amounts toapproximately a two (2) square-inch surface area. That is substantialconsidering how small the width of the “cathode contact area” is.Because of the relatively large contact surface area, the resistance ofthe contact is relatively small. This increases the current carryingcapacity of the contact, which can lead to much higher plating rates.Yet another advantage of the conductive fluid contact is that theelectrical contact is more uniform throughout the “cathode contactarea.” This results is a more uniform plating deposition across thesurface of the wafer. Still another advantage of the conductive fluid,particularly if it comprises sulfuric acid, is that typically theplating fluid also comprises sulfuric acid. Therefore, if the platingfluid leaked into the channel 458, it would not significantlycontaminate the conductive fluid, nor would it substantially affect theelectrical properties of the fluid. Although the conductive fluidcathode contact is advantageous, a mechanical contact can be also used.

G. Apparatus and Method of Plating a Wafer

1. Fluid Dynamics

a) Apparatus and Method for Directing Streams of Plating Fluid to theSurface of the Wafer

As previously discussed in Section I-A of the specification, one of theobjectives of the plating methodology of the invention is to provide arelatively fast plating rate. An aspect of the fluid dynamics of theplating method of the invention helps in achieving this objective. Thisaspect is forcibly directing fresh plating fluid toward the surface ofthe wafer while the wafer is immersed in a bath of plating fluid. Aspreviously explained, by directing fresh plating fluid toward thesurface of the wafer, the gradient of the ion concentration in the bathis increased. The current between the anode and the cathode isproportional to the ion concentration gradient within the bath. Inaddition, the current is, in turn, proportional to the plating rate.Accordingly, increasing the ion concentration gradient by forciblydirecting fresh plating fluid toward the surface of the wafer, increasesthe current, and therefore, increases the plating rate to provide arelatively fast plating rate. Furthermore, the constant directing ofplating fluid toward the surface of the wafer 308 continuouslyreplenishes the plating ions that are being depleted to form the platingdeposition.

Referring to FIGS. 15 and 17A, to effectuate this method of forciblydirecting fresh plating fluid toward the surface of the wafer 308, thecylinder/distribution ring assembly 304 comprises the cylinder wall 444having the lip seal ring 454 at its lower end to make a fluid sealcontact with the surface of the wafer 308 at the exclusion zone. Thecylinder/distribution ring assembly 304 also includes the additionalO-ring 445 for making a fluid seal contact with the wafer mounting base314. The combination of the cylinder wall 444, the wafer 308, and thelip seal ring 454 forms the container in which to support the platingfluid bath.

The cylinder/distribution ring assembly 304 also includes a distributionring 500 for forcibly directing fresh plating fluid toward the surfaceof the wafer 308 while the wafer is immersed in the plating fluid. Thedistribution ring 500 comprises a ring-shaped housing 502 connected tothe inner surface of the cylinder wall 444 in a coaxial manner. Themating of the housing 502 to the cylinder wall 444 forms an intakering-shaped cavity 504. The distribution ring 500 further includes atleast one feed port 506, preferably three, for receiving plating andrinsing fluid as well as clean dry air (CDA) from external sources, andcommunicating the fluids to the intake cavity 504. To direct the platingfluid toward the surface of the wafer 308, the distribution ring 500includes an annular slot 508 fluidly coupled to the intake cavity 504.The annular slot 508 is situated between the distribution ring 500 andthe cylinder wall so that the plating or rinsing fluid cascades down tothe surface of the wafer 308.

In operation, once the wafer 308 is in its full loading position and thecylinder/distribution ring assembly 304 is in a mating relationship withthe wafer mounting assembly 302, fresh plating fluid is introduced intothe intake cavity 504 by way of the plurality of feed ports 506. Theplating fluid quickly fills the intake cavity 504 and exits the cavityvia the annular slot and cascades down the cylinder wall 444, andcathode ring mount 442 toward the surface of the wafer 308. The platingbath begins to fill up with plating fluid immersing the anode assembly306 in plating fluid. The plating of the wafer can now begin.

Although the distribution ring 500 is attached to the cylinder wall 444in the preferred embodiment, it shall be understood that this need notbe the case. The distribution ring can be a separate assembly. Also, thedistribution ring 500 nor the cylinder wall 444 need not be cylindricalor ring-like shaped, but can encompass many other shapes includingrectangular, triangular, hexagonal shapes. The shape of the distributionring 500 and the cylinder wall 444 are not critical to the invention.Furthermore, the annular slot 508 need not be continuous, and cancomprise a plurality of orifices to form separate streams of fluid. Inaddition, the annular slot 508 need not be adjacent to cylinder wall 444but can be angled toward the center of the wafer 308.

b) Apparatus and Method for Effecting Random X-Y Direction Fluid Flow

As previously discussed in Section I-A of the specification, anotherobjective of the plating methodology of the invention is to provide asubstantially uniform plating deposition across the surface of thewafer. A second aspect of the fluid dynamics of the plating method helpsin achieving this objective. This second aspect is effecting randomhorizontal (x-y direction) of fluid flow within the plating fluid bath.As previously explained, the effecting of random x-y fluid flow withinthe bath prevents the formation of lengthy horizontal fluid flow acrossthe surface of the wafer. Since during plating, ions are continuouslybeing removed from the fluid bath, the ion concentration at thebeginning of a lengthy horizontal fluid flow is high. This results in ahigh ion deposit on the surface of the wafer at the beginning of alengthy horizontal fluid path. As the lengthy fluid flow continuous, itsion concentration is being depleted, therefore less plating ions aredeposited as the fluid flows across the surface of the wafer. As aresult, a gradient of deposited plating ions results across the surfaceof the wafer, which forms a non-uniform plating deposition. The randomx-y fluid flow reduces lengthy horizontal fluid flow which helps improvethe uniformity plating deposition on the wafer surface.

Referring to FIGS. 7, 19 and 21B, to effectuate random horizontal (x-ydirection) fluid flow within the plating fluid bath, the anode assembly306 includes one or more paddles 510 for randomly stirring the platingfluid bath. The plating apparatus 300 further includes a rotary assembly600 for effecting random rotation of the anode assembly 306 to cause thepaddles 510 to randomly stir the plating fluid bath. The anode rotaryassembly 600 comprises an electric motor 602 having a motor shaft 604rotatably coupled to an anode shaft 606 via a coupling 608. The motorshaft 604 and an upper portion of the anode shaft 606 are situatedcoaxially within a bearing housing 610. Preferably, the bearing housing610 includes two bearing sleeves 612 that separates the anode shaft 606from an inner wall of the bearing housing 610. In addition, the bearinghousing 610 preferably includes two O-rings 614 to prevent leakage intoand out-of the bearing housing 610. The lower end of the anode shaft 606is rotatably coupled preferably to the center of the anode assembly 306.

In operation, once the wafer 308 is in its full loading position, thecylinder/distribution ring assembly 304 is in mating relationship withthe wafer mounting assembly 302, and the plating fluid bath is formed,the electric motor 602 is actuated to rotate in a random manner. Therandom control of the motor 602 can be accomplished in many ways,preferably with a computer or microprocessor (not shown). With regard tothe random control, the motor speed can be varied randomly, as well asthe rotational direction (i.e. being clockwise or counter-clockwise) canbe varied randomly. The random rotation of the electric motor 602translates to a random movement of the paddles 510 via the motor shaft604, anode shaft 606, and the anode assembly 306. The random movement ofthe paddles 510 effectuates the random horizontal (x-y direction) fluidflow for improving the uniformity of the plating deposition across thesurface of the wafer.

Although the paddles 510 are part of the anode assembly 306 in thepreferred embodiment, it shall be understood that this need not be thecase. The paddles as well as the rotary assembly 600 need not beintegral with the anode assembly. In addition, the paddles 510 need notbe configured in a straight fashion, but can include random curvedsurfaces to further randomize the horizontal fluid flow of the platingfluid bath. Furthermore, the electric motor 602 can be of any type, forexample, it can a stepper motor, a direct current (DC) motor,alternating current (AC) motor, and others. The type of motor used isnot critical to the invention.

c) Apparatus and Method for Controlling Plating Fluid Path Flow

During the plating process, fresh plating fluid is continuously beinginjected into the bath through the distribution ring 500 to continuouslyreplenish the plating ions at the surface of the wafer 308. Because thevolume of the plating fluid bath is finite, the constant introduction ofplating fluid into the bath causes the bath to overflow. Thus, there isa need for an apparatus and method for controlling the plating fluidpath flow out of the bath. In addition, there is a need to recycle theplating fluid back to the distribution ring to prevent unnecessary wasteof the plating fluid.

Referring to FIGS. 7, 15 and 17A, to effectuate the method ofcontrolling plating fluid flow out of the bath and directing it to thesump area 310 for recycling thereafter, the cylinder/distribution ringassembly 304 includes one or more overflow slots 512 that is/are fluidlycoupled to a corresponding overflow duct 514 that leads down to the sumparea 310. The lower end of the overflow duct 514 is beveled to directplating fluid towards the wafer mounting base 314. In operation, duringthe plating process, plating fluid continuously overflows out of theplating bath into the overflow ducts 512. The overflow plating fluidthen enters the overflow ducts 514 and flows down towards the sump area310. The beveled end of the overflow ducts 514 directs the overflowedplating fluid onto the wafer mounting base 314 to cause a “cascadingflow” of the plating fluid down to the sump area 310 by way of thehousing 316. This cascading flow minimizes splashing and provides acontrolled manner of directing the plating fluid down to the sump area310.

2. Electrostatics—Anode

a) The Power Supply Electrical Connection to the Anode

For all the anode assemblies disclosed herein, there is a need toelectrically connect the positive terminal of the plating power supply(not shown) to the anode assembly 306. A uniqueness of the invention inaccomplishing this task is that it uses the same parts that performother functions involved in the plating process. These functions includerotating of the stirring paddles to effectuate random horizontal (x-ymovement) fluid flow within the plating fluid bath (Section II-G-b),rotating the anode assembly to dry the anode (Section II-I), and dryingthe wafer (II-K).

Referring to FIG. 19, the anode rotary assembly 600 incorporates ananode electrical connection assembly 620 used to provide an electricalconnection of the positive terminal of the plating power supply to theanode assembly 306. The anode electrical connection assembly 620comprises a connector 622 for connecting to the positive terminal of theplating power supply The connector 622 is electrically coupled to abrush 624 and a commutator 626. The commutator 626 is rotatably securedand electrically connected to the anode shaft 606. As previouslyexplained, the anode shaft 606 (which comprises an electrical conductor,such as titanium) is electrically coupled to the anode assembly 306.Accordingly, the positive anode voltage is communicated to the anodeassembly 306 via the connector 622, brush 624, commutator 626 and anodeshaft 606.

It shall be understood that there are many other ways of supplyingpositive voltage to the anode assembly. For instance, the anodeelectrical connection assembly 620 need not be part of the rotaryassembly 600, but could be a separate assembly, or incorporated withanother assembly.

b) Insoluble Anode

FIGS. 20A-B illustrate side and top views of an exemplary insolubleanode 650 in accordance with the invention. The insoluble anode 650 ispreferably configured into a metallic mesh. The insoluble anode,preferably comprising titanium plated with platinum, is configured intoa circular disk, and is subdivided into a plurality of peddles 652. Inthe preferred embodiment, there are six peddles 652. Each of the peddles652 are separated from each other by a slit 654 extending radially fromnear the center of the anode 650 to its perimeter. The anode 650 furtherincludes a though-hole 656 approximately its center to receive therein,in a secured fashion, the lower end of the anode shaft 606. The anode650 can be configured flat as shown in FIGS. 20A-B. Alternatively, thepeddles 652 can be bent or selectively shaped, as like in a propeller,to provide vertical fluid flow within the plating fluid bath or achieveany other desired fluid flow. In addition, the peddles 652 can also bebent or selectively shaped to adjust the electrostatic fields betweenthe anode and the cathode during plating, such as adjusting the fieldsin order to provide a substantially uniform current distribution acrossthe surface of the wafer, as discussed in Section I-B of thespecification.

Although in the preferred embodiment the insoluble anode 650 isconfigured in a circular shape, it shall be understood that it could beconfigured in many other configurations. The particular shape of theanode is not critical to the invention. It is preferred that the shapeof the insoluble anode be adjustable so that a desired electrostaticfields and/or fluid flow is formed. In addition, the insoluble anode 650need not be in a mesh form, but can comprise a solid sheet of metal. Nordoes the insoluble anode 650 need to have peddles 652 separated bycorresponding slits 654.

c) Soluble and Reconfigurable Anode (1) Angled-up Anode Configuration

FIGS. 21A-B illustrate top and cross-sectional views of a soluble anodeassembly 700 in an angled-up configuration in accordance with theinvention. The soluble anode assembly 700 comprises an anode mesh 702includes the main constituent of what is being deposited on the wafer.For example, if copper is to be deposited on the wafer, the anode mesh702 is preferably formed of a soluble phosphorized copper. In thepreferred embodiment, the soluble anode assembly 700 is configured intoa disk subdivided into a plurality of peddles 703 separated by slits705. The anode 702 is enclosed in an anode sleeve 704 used for filteringunwanted particles that are shed from the anode 702. The central portionof the anode 702 and sleeve 704 are secured to a corresponding centralportion of a base disk 706 by suitable fastening means, such as screws708. The outer ends of the anode 702 and sleeve 704 are sandwichedbetween a plurality of retaining clips 710 and corresponding spacers 712that are respectively secured together by suitable fastening means, suchas screws 714. The retaining clips 710 and spacers 712 are angularlyspaced around the anode assembly 700. Each spacer 712, in turn, issecured to a corresponding end of the base disk 706 by suitablefastening means, such as screw 716. The base disk 706 includes acentrally located clearance hole 718 for receiving therethrough an endof the anode shaft 606. A securing nut 720 is threaded coaxially overthe end of the anode shaft 606 to secure the anode shaft 606 to theanode assembly 700. The base disk 706 may integrally incorporate thestirring paddles 510 as previously explained in Section 11-G-1-b of thespecification.

The anode assembly 700 further includes a ring-shaped flange 722 that issecured and electrically coupled to the anode 702 by way of suitablefastening means, such as screws 708. A resilient contact clip 724includes a lowered section that is secured to the flange 722 by way ofsuitable fastening means, such as screws 726. The upper end of thecontact clip 724 contacts the anode shaft 606 to effectuate anelectrical connection between the anode 702 and the anode shaft 606. Inthis configuration, the anode 702 is oriented in an angled-up manner.This is because there is a relatively small space between the center ofthe anode 702 and the center of the base disk 706 since there is anabsence of a spacer there, and there is a relatively large spacingbetween the end of the anode 702 and the base disk 706 due to the spacer712. As explained in Section I-B of the specification, thisconfiguration of the anode 702 may substantially equalize the currentsacross the surface of the wafer so as to provide a substantially uniformplating deposition across the wafer.

(2) Angled-down Anode Configuration

One of the advantage of the soluble anode assembly 700 of the inventionis that it can be easily reconfigurable to alter the distribution of theelectrostatic lines between the anode and the cathode, as discussed inSection I-B of the specification. The reconfiguration of the anode 702is useful when the plating environment has changed, such as when adifferent plating metal (other than copper) is used, or when the platingconcerns a new type of wafer or article, such as a ceramic wafer, orwhen the cathode configuration has changed. Because of possible changesin the plating environment, there is a need to experiment with the anodeconfiguration to achieve the desired uniformity in the platingdeposition. The anode assembly 700 of the invention easily allows forthe reconfiguration of the anode for this purpose.

FIGS. 22A-B illustrate top and cross-sectional views of a soluble anodeassembly 700′ in an angled-down configuration in accordance with theinvention. The angled-down anode assembly 700′ includes essentially thesame parts as that of the angled-up assembly 700, and those parts havethe same reference numbers. The anode-down assembly 700′ differs in thatthere is an absence of spacers at the end of the anode 702. Accordingly,the end of the anode 702 and sleeve 704 are sandwiched between theretaining clip 710 and the base disk 706 secured together by suitablefastening means, such as screw 730. In addition, the anode-down assembly700′ differs in that there is a spacer 732 situated between the centerof the anode 702 and the center of the disk base 706. Suitable fasteningmeans secure the center of the anode 702 and sleeve 704 to the spacer732, and secure the spacer 732 to the center of the base disk 706, suchas screws 732 and 734, respectively.

As FIGS. 21 and 22 illustrate, the anode assembly 700 can be configuredinto an angled-up or angled-down orientation by appropriate placing ofspacers. This is performed prior to performing several experimental runsto determine which configuration of the anode assembly 700 is moresuitable for the application at hand. The spacers need not be of anyparticular height, but can encompass a wide range of heights so that thedegree that the anode is angled-up or angled down can be varied. Asexplained in Section I-B, the angled-down anode assembly 700′ may beuseful where the cathode is in connected to the center of the wafer, aconfiguration that is not preferred. There may also be otherapplications where the angled-down is more suited for the platingprocess.

(3) Flat Anode Configuration

FIGS. 23A-B illustrate top and cross-sectional views of a soluble anodeassembly 700″ in a flat configuration in accordance with the invention.The flat anode assembly 700″ includes essentially the same parts as thatof the angled-up and angled down assemblies 700 and 700′, and thoseparts have the same reference numbers. The flat anode assembly 700″differs in that there is an absence of spacers at the end and at thecenter of the anode 702. The center of the anode 702 and sleeve 704 isconnected to the center of the disk base 706 in the same manner providedin the angled-up assembly 700. Also, the end of the anode 702 and sleeve704 are secured to the end of the disk base 706 in the same mannerprovided in the angled-down assembly 700′. Again, there may beapplications where the flat anode assembly 700″ is more suitable for theplating process, than the others assemblies 700 and 700″. This can bedetermined by performing several experimental runs and inspecting thewafer for plating uniformity and other characteristics.

(4) Anode Assembly with Shield

FIG. 23C illustrates cross-sectional view of a flat anode assembly 700′″similar to soluble anode assembly 700″ as described above. Accordingly,the common elements are designated with the same reference numbers. Theflat anode assembly 700′″ differs from assembly 700″ in that itadditionally includes a lower shield 728 and an upper shield 732. In thepreferred embodiment, the lower shield 728 is mounted to the base 706 bysuitable fastening means, such as screw 730. Also, the upper shield 732is mounted to the base 706 by suitable fastening means, such as screw732.

In the preferred embodiment, the lower shield 728 includes a portion 736that is situated substantially parallel to the base 706 and covers itslower perimeter region. The lower shield 728 includes a more centralportion 738 that angles below and towards the center of the anodeassembly 700′″. As a result of this configuration, an electrostatic holeis formed at the center region of the anode assembly 700′″ that channelsthe electrostatic field lines from the anode to the cathode. Asexplained with Section I-B of the specification with reference to FIG.5B, the lower shield 728 is used to configure the electrostatic fieldsbetween the anode and the cathode to provide a more uniform current flowacross the surface of the wafer.

In the preferred embodiment, the upper shield 732 comprises a portion740 that is situated substantially parallel to the base 706 and coversits upper perimeter region. The upper shield 732 also includes a morecentral portion 742 that extends vertically upwards from the anodeassembly 700′″ to slightly above the lower end of the bearing housing610. The upper shield 732 reduces stray electrical currents that wouldotherwise form within the plating fluid above the anode assembly 700′″.

Although the upper and lower shields 728 and 732 is shown being usedwith the flat anode assembly 700″, it shall be understood that theshields can also be used with the angled-tip anode assembly 700 and theangled-down anode assembly 700′. In addition, the shields 728 and 732can also be used with the insoluble anode assembly 650. Furthermore,these anode assemblies need not have both the lower and upper shields728 and 732, but can have either the lower shield 728 or the uppershield 732. Finally, the lower and upper shields 728 and 732 need not beconfigured in the manner shown in FIG. 23C, but can include any of anumber of shapes to achieve the desired shielding and shaping of theelectrostatic field lines between the anode and the cathode

(5) Secondary Anode/Cathode Ring (a) Anode Mode

When the plating fluid is initially introduced into the bath by thedistribution ring 500, it takes some time to fill the bath andthereafter begin the plating process. Thus, the plating fluid initiallycontacts the surface of the wafer without being exposed to the positivedifference between the anode and cathode, and consequently, no currentflow is formed at this point. As a result, the acidic properties of theplating fluid begins to etch the surface of the wafer 308, therebyreducing and/or eliminating the thickness of the copper seed layer ofthe wafer 308. For the copper-plating embodiment of the platingapparatus 300, without the copper seed layer, proper plating of thewafer 308 cannot occur.

Referring now to FIGS. 17A-B, a secondary anode/cathode ring assembly740 is provided to prevent acidic damage to the copper seed layer of thewafer 308 from the inactivated plating fluid that is in contact with thewafer prior to the primary anode energizing the plating fluid. In thepreferred embodiment, the secondary anode/cathode ring assembly 740 isconfigured into an annular electrically conductive ring mounted to thevertical surface of the cathode ring mount 442 by suitable means, suchas electrically conductive screw 742. An O-ring 744 is placed around thethreaded-portion of the screw 742 in between the screw head and thecathode ring mount 442 in order to prevent fluid leakage therethrough. Awire 746 is routed from the positive terminal of a power supply (notshown) to the screw 742 by way of the spaced between the cathode ringmount 442 and the cathode ring 440 in order to supply positive voltage(in anode mode) to the secondary anode/cathode ring 740.

In operation, when the plating fluid is initially introduced into thebath by the distribution ring 500, the secondary anode/cathode ring 740is energized with a positive voltage in order to activate the platingfluid that initially accumulates at the surface of the wafer 308.Because the plating fluid is activated, it prevents the acidicproperties of the plating fluid from damaging the copper seed layer ofthe wafer 308. At this time, there may be some plating deposited on thesurface of the wafer 308. When the plating fluid in the bath rises abovethe primary anode, the positive voltage on the secondary anode/cathodering 740 is removed, and the primary anode 306 is energized to performthe plating of the surface of the wafer 308. Accordingly, this solvesthe problem of the plating fluid causing acidic damage to the copperseed layer of the wafer 308 before the plating of the wafer begins.

Although in the preferred embodiment the secondary anode/cathode ring740 is configured into an annular ring, it shall be understood that manyother configurations for the secondary anode/cathode ring are possible.The only requirement is that the secondary anode/cathode ring 740 isnear the bottom of the plating fluid bath so that it energizes theplating fluid that initially accumulates near the surface of the wafer308. Nor does the secondary ring need to be mounted on the cathode ringmount 442, but any suitable place near the surface of the wafer. In thepreferred embodiment, more than one wire/screw is used to supplypositive voltage to the secondary anode/cathode ring 740. There are anumber of ways to supply positive voltages to the secondaryanode/cathode ring 740, all of which are not critical to the invention.

(b) Cathode Mode

Generally, the copper seed layer of the wafer 308 is relatively thin. Itmay have a thickness in the range of about 200 to 1500 Angstroms.Because the copper seed layer is relatively thin, the resistance of thelayer is relatively high. This characteristic of the copper seed layeradversely affects the initial plating of the wafer. More specifically,because of the high resistance property of the copper seed layer, theplating current through the center region of the wafer towards thecathode at the perimeter of the wafer is relatively small compared tothe plating current that flows directly to the perimeter of the wafer.As a result, more plating deposition occurs near the perimeter of thewafer than at the center region of the wafer. Thus, there is a need tocompensate for this uneven plating deposition across the surface of thewafer.

Not only is the secondary anode/cathode ring 740 useful in an anode modeto prevent acidic damage of the copper seed layer as described above,the secondary anode/cathode ring 740 serves in a cathode mode toameliorate the problem of uneven plating deposition due to the highresistance property of the copper seed layer. During initial plating ofthe wafer 308, a negative voltage with respect to the voltage on thecathode is applied to the secondary anode/cathode ring 740. Since thesecondary anode/cathode ring 740 is radially around the perimeter of thewafer 308, the more negative voltage on the ring 740 diverges theplating ions drawn to the perimeter of the wafer 308 towards the ring740. As a result, the plating rate at the perimeter of the wafer 308 isreduced so that it is more even with the plating rate at the centerregion of the wafer 308. Thus, this technique can achieve a more uniformplating deposition across the surface of the wafer 308. In general, thesecondary anode/cathode ring 740 can be used to alter the electrostaticfield formed between the anode 306 and the cathode 440 to control theplating of the wafer 308.

An additional application of the secondary anode/cathode ring 740 is toremove plating ions off a desired region of the wafer 308. In accordancewith this application, the voltage on the primary anode 306 is removedso as to remove the electrostatic field between the anode 306 and thecathode 440. Then, a negative voltage with respect to the voltage on thecathode 440 is applied to the secondary anode/cathode ring 740. Whenthis occurs, the cathode 440 operates as an anode and the secondaryanode/cathode ring 740 operates as a cathode. Accordingly, the negativevoltage on the secondary anode/cathode ring 740 causes the removal ofplating ions off the wafer surface and deposits the removed plating ionson the secondary anode/cathode ring 740.

This application is particularly useful in removing excess plating offthe perimeter region of the wafer 308 after the wafer has undergone theplating process. In some situations, there may be an increased buildupof plating deposition at the perimeter region of the wafer 308, due to,for example, the high resistance property of the seed layer on thesurface of the wafer. If this occurs, it would be desirable to removesome of the excess plating at the perimeter region of the wafer 308 soas to better even out the plating deposition across the surface of thewafer. To do this, a negative voltage with respect to the cathode 440 isapplied to the secondary anode/cathode ring 740. Since the secondaryanode/cathode ring 740 is situated generally coincident with theperimeter of the wafer 308, the negative voltage on the secondaryanode/cathode ring 740 removes excess plating off the perimeter regionof the wafer 308, to better even out the plating deposition across thesurface of the wafer 308. In general, an electrical conductor with adesired voltage applied to it can be positioned near the wafer 308 toremove plating at any desired region of the wafer surface.

(6) Electrostatics—Cathode

Most of the discussion relating the electrostatics aspect of the platingmethod of the invention that pertains to the cathode was given inSection II-G of the specification. It is worthy to restate that theunique cathode contact of the invention improves the uniformity of theplating deposition across the surface of the wafer, as well as improvesthe plating rate. The uniformity of the plating is improved by providinga uniform cathode contact along the “cathode contact area” of theexclusion zone of the wafer. This can be accomplished with the use of aconductive fluid or with a plurality of equally-spaced mechanicalcontacts. Because of the uniformity of the cathode contact, the surfacecurrents across the wafer are more uniform, which improves theuniformity of the plating. The plating rate of the plating is improvedby providing a large contact area along the “cathode contact area” ofthe exclusion zone of the wafer. The continuous contact of theconductive fluid or the almost-continuous contact of the mechanicalcontacts along the “cathode contact area” of the exclusion zone providesa large contact area that can handle large currents, which can improvesthe plating rate.

Referring to FIG. 24, another aspect of the cathode contact to thesurface of the wafer is providing a cathode electrical connectionassembly 750 to effectuate the electrical connection of the negativeterminal of the plating power supply to the cathode ring 440. Thecathode electrical connection assembly 750 comprises a connector 752mounted to the top horizontal mounting plate 404 for making anconnection to the negative terminal to the power supply (not shown). Afirst end of a wire 754 is electrically connected to the connector 752and is routed downward towards the cathode ring 440 through a hole 756in the top mounting plate 404. A portion of the wire 754 is configuredinto a stress-relief loop 758 and a subsequent portion is situatedwithin a duct 760 extending vertically along the outside of the cylinderwall 444. The opposing end of the wire 754 is connected to a lug 762attached to the cathode ring 440 by screw 764. Accordingly, the negativecathode voltage is communicated to the cathode ring 440 via theconnector 752, wire 754 that has a stress-relief loop 758 and extendsthrough duct 760, lug 762, and screw 764. There are preferably threecathode electrical connection assemblies 750 angularly spaced around thecylinder/distribution ring assembly 304.

H. Apparatus and Method of Draining the Plating Fluid Bath

Once the plating of the wafer 308 is completed, the next procedure inthe overall plating process is to drain the plating fluid from the bath.Prior to draining the plating fluid bath, the anode and/or cathodevoltage(s) is/are removed from the anode and cathode, and the rotationof the anode assembly 306 is ceased. Thus, prior to draining the platingfluid bath, the cylinder/distribution ring 304 is making a fluid sealcontact with the wafer mounting assembly 302, the wafer 308 is in itsfull loading position, and the bath is filled with plating fluid.

FIG. 25 illustrates the plating apparatus 300 in a plating fluiddraining position in accordance with the invention. After completion ofthe plating process as described in the previous paragraph, theshort-stroke pneumatic actuator 412 is actuated to move vertically toits full raised position. The vertical movement of the short-strokepneumatic actuator 412 causes the mounting plate 414 to move upward withthe actuator 412. This action causes the long-stroke pneumatic actuator410 to similarly move upward. The length of the vertical movement of theshort-stroke pneumatic actuator 412 is such that it is larger than theclearance that exists between the extender shoulder 428 and the coupling406, when the extender 428 is at its full lowered position. Accordingly,the vertical movement of the actuator 412 causes the shoulder 428 tolift the cylinder/distribution ring assembly 304 off the wafer mountingassembly 302.

The lifting of the cylinder/distribution ring assembly 304 off the wafermounting assembly 302 causes the plating fluid to drain out through theperimeter of the wafer 308. The plating fluid then cascades down thewafer mounting base 314 and housing 316 to the sump area 310. At thistime, the sump valve 812 is opened to allow the plating fluid to draininto a reservoir (not shown) for later use, as will be discussed in moredetail in Section II-L of the specification. The draining of the platingfluid bath is ceased when most of the plating fluid has drained out ofthe sump area 310.

I. Apparatus and Method of Drying the Anode Assembly

Referring again to FIG. 25, concurrently with or after the draining ofthe plating fluid bath, there is a need to remove any excess platingfluid that remains on the anode assembly 306. Accordingly, the platingapparatus 300 includes a nozzle 770 directed at the anode assembly 306.In the preferred embodiment, the nozzle 770 communicates forced nitrogengas to the anode assembly 306. Since the center of the anode assembly306 comprises a plurality of small components, it is preferred that thenozzle 770 is aimed towards the center of the anode assembly 306. Inoperation, the electric motor 602 is actuated to cause a high-speedrotation of the anode assembly 306 in order to spin-off some of theplating fluids. At the same time, the nozzle 770 directs forced nitrogengas towards the center of the anode assembly. This process continuesuntil most of the excess plating fluid is removed from the anodeassembly 306.

J. Apparatus and Method of Rinsing the Wafer After Plating

Once the plating fluid has sufficiently drained out of the bath inaccordance with Section II-H, the next procedure in the overall platingprocess is to rinse the wafer 308. After the draining of the platingfluid, the top surface of the wafer 308 will have some plating fluid onit. Thus, there is a need to rinse off the remaining plating fluid offthe top surface of the wafer 308. In addition, the underside of thewafer 308 may also be in contact with contaminants, therefore, there isalso a need to rinse off the underside of the wafer. In this Section ofthe specification, the preferred manner of rinsing of the top-side andunderside of the wafer 308 is discussed.

Referring to FIG. 18, before the rinsing of the wafer 308 can occur, andin fact, preferably before the cylinder/distribution ring assembly 304is lifted to drain the plating fluid bath, it is desired that theconductive fluid in the conductive channel 458 and correspondingfeed/drain line 460 be drained and flushed out by DI-water. This is toprevent contamination of the conductive fluid from the plating fluidsince this area would be expose to the plating fluid during drainage.Accordingly, before the cylinder/distribution ring assembly 304 islifted, the conductive fluid is allowed to drain from the conductivechannel 458 and feed/drain lines 360 into a suitable reservoir (notshown). Then DI water is forcibly injected into the conductive channel458 and feed/drain line 460 in order to flush out this area.

Referring now to FIG. 25, after the cylinder/distribution ring assembly304 is lifted to drain the plating fluid, the first step in the rinsingof the wafer 308 is to supply DI water to the distribution ring 500 sothat the ring directs the DI water to the top surface of the wafer 308.The DI water removes the plating fluid remaining on the top-surface ofthe wafer 308, and consequently drains down to the sump area. Therinsing of the top-surface of the wafer 308 is continued until thetop-surface of the wafer 308 has been sufficiently rinsed.

Referring to FIG. 26, the next step in the preferred method of rinsingthe wafer 308 is to rinse the underside of the wafer. First, thewafer-supporting fluid bed is drained through the feed/drain line 362.After this occurs, the motor 334 of the wafer lift assembly 320 isactuated in order to raise the wafer-supporting posts 322 slightly.Consequently, the wafer 308 is lifted off the wafer mounting base 314.Then, DI water is injected upon the underside of the wafer 308 by way ofthe feed/line 362 in order to rinse the underside of the wafer. Thespace between the wafer 308 and the wafer mounting base 314 allows theDI water to drain out of the fluid bed cavity 356, out the perimeter ofthe wafer 308, and down to the sump area 310. The rinsing of theunderside-surface of the wafer 308 is continued until it has beensufficiently rinsed.

K. Apparatus and Method of Drying the Wafer

Referring back to FIG. 18, during the rinsing of the wafer 308 asdiscussed in the previous section, rinsing solution accumulates in thefeed/drain line 460 of the conductive fluid. It is undesirable to haverinsing solution remaining in the feed/drain line 460 since it willcontaminate the conductive fluid during the next plating process.Therefore, there is a need to purge out the rinsing solution from thefeed/drain line 460. In the preferred embodiment, this is performed byinjecting hot (above ambient temperature) nitrogen gas up through thefeed/drain line 460 so as to force the remaining rinsing solution out ofthe feed/drain line 460. This process is continued until the feed/drainline 460 is sufficiently dried.

Referring to FIGS. 19 and 25, the apparatus for performing the drying ofthe wafer 308 in accordance with the invention comprises thedistribution ring 500 for directing hot (above ambient temperature)nitrogen gas upon the top surface of the wafer 308. The wafer dryingapparatus also comprises a nozzle 780 mounted to the top of the bearinghousing along with the motor 602. The nozzle 780 is fluidly coupled to achannel 782 within the bearing housing 610 that leads to the anode shaft606. The anode shaft 606 includes an orifice 784 within the bearinghousing 610 that is fluidly coupled to the channel 782. The anode shaft606 includes a channel 786 extending coaxially within that leads to anopening at the lower end of the anode shaft. Finally, the wafer dryingapparatus further includes the feed/drain line 360 situated below thewafer 308.

In operation, hot (above ambient temperature) nitrogen gas is introducedinto the distribution ring 500 from one or more of its feed ports 506.The distribution ring 500 directs the hot nitrogen gas towards the topsurface of the wafer 308 by way of its intake cavity 504 and its annularslot 508 This process is performed for a desired period of time. Then,hot nitrogen gas in introduced into nozzle 780 to direct it to the topsurface of the wafer 308 by way of channel 782 within the bearinghousing, orifice 784 of the anode shaft 606, channel 786 within theanode shaft 606, and the opening at the bottom of the anode shaft 606.This is again performed for a desired period of time. Both the abovedescribed drying steps is performed to sufficiently dry the top surfaceof the wafer 308.

Then hot nitrogen gas is introduced into the feed/drain line 360 inorder to forcibly direct the gas upon the underside of the wafer. Thisis performed for a desired period of time in order to sufficiently drythe underside of the wafer 308. Once the wafer 308 is sufficientlydried, the feeding of the nitrogen gas is ceased. The order by which thenitrogen gas is used to dry the top and bottom side of the wafer 308 isnot critical to the invention.

L. Apparatus and Method of Draining Fluids From the Plating Apparatus

During the plating and rinsing processes described above, it is desiredthat the plating apparatus and method of the invention provides a meansfor draining the plating and rinsing fluids after they have been used.With regard to the plating fluid, it is desirable that the plating fluidbe recycled back to the distribution ring for use again in the platingprocess. Thus, there is a need to accumulate the plating fluid that hasalready been used during the plating process, filter the used platingfluid so that it can be recycled back the plating fluid to thedistribution ring for reuse again by the plating process. With regard tothe rinsing solution, it is desirable that the rinsing solution beproperly disposed of after the wafer has undergone the rinsing process.Thus, for both the plating and rinsing fluids, there is a need tocontrol the fluids after they have been used in their respectiveprocesses.

Referring to FIGS. 25 and 27, the sump 310 of the plating apparatus 300achieves the preferred method of controlling the fluid flow after theyhave been used in their respective processes. As previously discussed,the plating apparatus 300 is designed such that during the draining ofthe plating and rinsing fluids and the overflow of the plating fluidduring the plating process, the corresponding fluids flows down to thesump 310 by way of the wafer mounting base 314 and the wafer-mounthousing 316. The sump 310 preferably includes an inclined base 810situated at the bottom of the wafer-mount housing 316. The sump 310further includes a sump valve 812 situated at the lowest portion of theinclined base 810. The sump valve 812 is preferably of the type thatcomprises an input port and two output ports. The input port of sumpvalve 812 receives both the used plating and rinsing fluids. One of theoutput ports of the sump valve 812 is for directing the rinsing fluid toa disposal area (not shown). The other output port of the sump valve 812is used for directing the plating fluid to a recycling reservoir (notshown).

FIGS. 28A-B illustrate top and side cross-sectional views of thepreferred embodiment of sump valve 812. The sump valve 812 comprises aninput port 814 for receiving the used plating and rinsing fluids, afirst output port 816 fluidly coupled to a rinse waste tank (not shown),and a second output port 818 fluid coupled to a plating tank (notshown). The sump valve 812 comprises a switch 820 for selectivelycoupling the input port 814 to one of the output ports 816 and 818. Inthe preferred embodiment, the switch 820 comprises a pneumatic cylinder822 axially coupled to a piston 824 that is situated within a borehousing 826 of the sump valve 812. The piston 824 includes an occludingshoulder 828 that makes a fluid seal contact using an O-ring 830 withthe inside walls of the bore housing 826. The pneumatic cylinder 822 canbe actuated to position occluding shoulder 828 on one side of the inputport 814 that is closer to the rinsing fluid output port 816 to occludefluid flow to that port, and allow fluid flow to the plating fluidoutput port 818. Similarly, the pneumatic cylinder 822 can be actuatedto position occluding shoulder 828 on one side of the input port 814that is closer to the plating fluid output port 818 to occlude fluidflow to that port, and allow fluid flow to the rinsing fluid output port816.

In operation, during and after the plating of the wafer 308 when platingfluid is allowed to overflow and drain, the plating fluid is directed tothe sump 310 by way of cascading down the wafer mounting base 314 andthe wafer-mount housing 316. The plating fluid then encounters theinclined base 810 of the sump 310 and flows down to the input port 814of the sump valve 812. Prior to this overflowing and draining of theplating fluid, the pneumatic cylinder 822 is actuated to position theoccluding shoulder 828 of the piston 824 to fluidly couple the inputport 814 with the plating fluid output port 818. Thus, as the platingfluid enters the input port 814 of the sump valve 812, it is directed tothe plating fluid output port 818 to which the plating tank is fluidlycoupled.

After the rinsing of the wafer 308 when the rinsing fluid is allowed todrain, the rinsing fluid is directed to the sump 310 by way of cascadingdown the wafer mounting base 314 and the wafer-mount housing 316. Therinsing fluid then encounters the inclined base 810 of the sump 310 andflows down to the input port 814 of the sump valve 812. Prior to thedraining of rinsing fluid, the pneumatic cylinder 822 is actuated toposition the occluding shoulder 828 of the piston 824 to fluidly couplethe input port 814 with the rinsing fluid output port 816. Thus, as therinsing fluid enters the input port 814 of the sump valve 812, it isdirected to the rinsing fluid output port 816 to which the rinsing tankis fluidly coupled.

M. Apparatus and Method of Controlling and Disposing of Fumes

The plating of the wafer 308 typically produces potentially corrosivefumes that accumulate within the plating apparatus 300. The source ofthese fumes is primarily the plating fluid. Because of environmentalconcerns and regulations, there is a need to contain the fumes and toprovide a controlled manner of expelling the fumes from the platingapparatus 300. The plating apparatus and method of the inventionprovides this control containment and expulsion of fumes created duringthe plating process.

Referring to FIG. 25, in order to contain the fumes created within theplating apparatus, the plating apparatus 300 provides hermetic sealingthroughout the plating compartment. For example, the mating of theflexible boot 408 with the top horizontal mounting plate 404 forms ahermetic seal therebetween. The mating of the flexible boot 408 and thetop of the cylinder wall 444 also forms a hermetic seal therebetween.Finally, the cathode ring mount 442 includes an annular extension 850having its annular end situated within an annular recess 852 formedwithin a lower horizontal plate 856. A liquid seal is introduced intothe recess 852 by way of feed line 858 which immerses the lower end ofthe annular extension 850. The liquid seal forms a hermetic sealing withthe annular extension 850 to prevent fumes from escaping therethrough.In the preferred embodiment, the liquid seal comprises DI-water.

The use of the liquid seal assists in the alignment of the cathode ring440 to the wafer 308 during the lowering of the cylinder/distributionring assembly 304 down to the wafer mounting assembly 302. As previouslydiscussed in Section II-E of the specification, in order to achieve thedesired alignment of the cathode ring 440 to the wafer 308, it ispreferred that the cylinder/distribution ring assembly 304 be compliantin the lateral direction (i.e. x-y direction), and restricted in therotational direction. The liquid seal allows the lowering of thecylinder/distribution ring assembly 304 to be compliant in the lateraldirection since liquid tends to displace when a solid object moveswithin it. As previously discussed, the compliancy in the lateraldirection of the cylinder/distribution ring assembly 304 allows theassembly 304 to “self-align” as it is lowered onto the wafer mountingassembly 302.

Referring to FIGS. 16, 25 and 27, to provide a control expulsion of thefumes, the plating apparatus 300 includes a feed line 860 near the sump310 to forcibly introduce clean dry air (CDA) into the platingcompartment. The plating apparatus 300 further includes a plurality ofexhaust ports to expel the fumes from the plating compartment. Withreference to FIG. 16, the top horizontal mounting plate 404 includes anexhaust port 862 for the plating fumes. With reference to FIG. 27, thesump 310 also includes exhaust ports 864 for the plating fumes. Theseexhaust ports 862 and 864 may be connected to some hose (not shown) forproviding a controlled manner of expelling the fumes from the platingapparatus.

N. Apparatus and Method of Unloading the Wafer

After the plating of the wafer 308 has been completed, and it has beenrinsed and dried, the next step in the overall plating process is tounload the wafer 308 from the plating apparatus 300. The procedure forunloading the wafer 308 is similar to the loading procedure, only in thereverse direction. The position of the plating apparatus 300 prior tothe unloading of the wafer 308 is that the cylinder/distribution ringassembly 304 is in its fluid draining position, the wafer 308 is also inits fluid draining position (i.e. slightly above the final loadingposition), and the wafer supporting posts 322 are making vacuum contactwith the underside of the wafer 308.

With reference to FIG. 25, the first step in the method of unloading thewafer 308 is raise the cylinder/distribution ring assembly 304 to itsfull raised position as shown in FIG. 8. This is accomplished byactuating the long-stroke pneumatic cylinders 410 to retract theirrespective pistons 424 and cause the corresponding extenders to lift thecylinder/distribution ring assembly 304 to its full raised position.This action forms the clearance region 311 between thecylinder/distribution ring assembly 304 and the wafer mounting assembly302 in order for the wafer loader 312 to be introduced therebetween.

With reference to FIG. 11, the next step in the method of unloading thewafer 308 is to raise the wafer 308 to its full raised position. This isaccomplished by actuating the motor 334 to raise the wafer supportingposts 322 to its full raised position. Once this has occurred, the waferloader 312 is introduced into the plating apparatus 300, andspecifically, directly below the wafer 308. Then, the vacuum contact ofthe wafer supporting posts 322 and the underside of the wafer 308 isremoved.

With reference to FIG. 9, the next step in the method of unloading thewafer 308 is to lower the wafer 308 onto the wafer loader 312. This isaccomplished by actuating the motor 334 to lower the wafer supportingposts 322 to its full lowered position. This action causes the wafer 308to drop onto the wafer loader 312. Once this has occurred, the waferloader 312 is then removed from the plating apparatus 300 to producedthe final product, i.e. a wafer that has a substantially uniform platingdeposition produced by the apparatus and methods of the invention.

Apparatus and Method of Cleaning the Plating Apparatus

With reference to FIGS. 8 and 16, in order to clean the platingapparatus 300 after performing a plating process, the plating apparatus300 includes one or more nozzles 900 for spraying the platingcompartment with DI-water in order to clean most of the surfaces. Thenozzles 900 are mounted within holes 902 formed through the tophorizontal mounting plate 404. The top horizontal mounting plate 404 mayalso include feed ports for introducing clean dry air (CDA) and nitrogengas to the distribution ring 500 as desired.

P. Conclusion

While the invention has been described in connection with variousembodiments, it will be understood that the invention is capable offurther modifications. This application is intended to cover anyvariations, uses or adaptation of the invention following, in general,the principles of the invention, and including such departures from thepresent disclosure as come within known and customary practice withinthe art to which the invention pertains.

It is claimed:
 1. In a plating apparatus comprising a container, acathode electrode, an anode electrode situated at a higher positionwithin said container, and an intermediate electrode situated at anintermediate position within said container below said higher position,a method of plating an article situated at a lower position within saidcontainer below said intermediate position and having a metal seed layerin electrical contact with said cathode electrode, comprising:introducing plating fluid into said container to form a plating fluidbath; forming a positive voltage potential from said intermediateelectrode to said cathode when said plating fluid bath is in contactwith said intermediate electrode but not in contact with said anodeelectrode, wherein said positive voltage activates said plating fluidbath to reduce acidic etching of said metal seed layer; and forming asecond positive voltage potential from said anode electrode to saidcathode electrode when said plating fluid bath is in contact with saidintermediate and anode electrodes, wherein said second positive voltagecauses plating deposition to occur over said metal seed layer.
 2. Themethod of claim 1, wherein said article comprises a wafer.
 3. The methodof claim 1, wherein said metal seed layer comprises copper.
 4. Themethod of claim 1, wherein said intermediate electrode is configuredinto an annular ring.
 5. The method of claim 1, wherein said cathodeelectrode is situated within said container.
 6. In a plating apparatuscomprising a container, a cathode electrode, an anode electrode situatedat a higher position within said container, and an intermediateelectrode situated at an intermediate position within said containerbelow said higher position, a method of plating an article situated at alower position within said container below said intermediate positionand having a metal seed layer in electrical contact with said cathodeelectrode, comprising: introducing plating fluid into said container toform a plating fluid bath; forming a positive voltage potential fromsaid intermediate electrode to said cathode when said plating fluid bathis in contact with said intermediate electrode but not in contact withsaid anode electrode, wherein said positive voltage activates saidplating fluid bath to reduce acidic etching of said metal seed layer;removing said positive voltage potential; and forming a second positivevoltage potential from said anode electrode to said cathode electrodewhen said plating fluid bath is in contact with said intermediate andanode electrodes, wherein said second positive voltage causes platingdeposition to occur over said metal seed layer.
 7. The method of claim6, wherein said article comprises a wafer.
 8. The method of claim 6,wherein said metal seed layer comprises copper.
 9. The method of claim6, wherein said intermediate electrode is configured into an annularring.
 10. The method of claim 6, wherein said cathode electrode issituated within said container.